What does acinus mean?
An acinus is one of the minute, berry-shaped units that make up certain glands and the deep structure of the lungs. In glandular tissue, such as the pancreas or salivary glands, an acinus is a cluster of secretory cells arranged around a central space, releasing enzymes or other substances into ducts. In respiratory anatomy, the term refers to the region of the lung served by a single terminal bronchiole, encompassing the alveoli where oxygen and carbon dioxide are exchanged. The word comes directly from the Latin acinus, meaning 'berry' or 'grape', reflecting the way these structures cluster like fruit on a stem. Almost entirely confined to medical and biological contexts, acinus appears most often in its plural form, acini, when histologists describe gland architecture. Its adjective forms, acinar and acinic, are common in phrases such as 'acinar cells'. Though obscure to general readers, the word is fundamental to understanding how glands and lungs are organized at the microscopic level.
nounOne of the small, berry-shaped terminal sacs or lobules of a gland (such as the pancreas or salivary glands) or of the lung, where secretion or gas exchange takes place.
- The terminal secreting portion of a gland, consisting of a cluster of secretory cells around a lumen (e.g. in the pancreas or salivary glands).
- In respiratory anatomy, the portion of the lung supplied by one terminal bronchiole, including its alveoli; the basic gas-exchange unit of the lung.
"Under the microscope, each pancreatic acinus appeared as a compact cluster of secretory cells surrounding a tiny central lumen."
"Damage to the acini of the pancreas can impair the production of digestive enzymes."
"Each pulmonary acinus functions as the primary site where oxygen passes into the blood."
The plural follows the Latin second-declension pattern (-us → -i) and is strongly preferred over the anglicized 'acinuses' in medical and scientific writing.
"The pancreas contains thousands of acini, each contributing enzymes to the digestive duct system."
Latin for 'berry', acinus earned its name because these tiny glandular sacs cluster together like grapes on a stem.
Reviewed by Deb Chak, Editor. AI-assisted content curated by RJS Tech Solutions LLP.
Etymology of acinus
Acinus was borrowed in the early modern period directly from Latin, where acinus meant 'berry' or 'grape', and ultimately traces back to the Greek akis, meaning a point or dart, via the notion of a small pointed seed. Anatomists adopted the term because the clustered secretory sacs of glands resemble bunches of grapes. The same Latin root survives in the Romance languages, as in Italian acino, meaning a single grape or berry.
Related word forms
How acinus is actually used
A technical term used almost exclusively in anatomy, histology, and medicine; it rarely appears outside scientific writing. The plural 'acini' is standard in professional literature, while 'acinuses' is uncommon.
Easily confused with acinus
An alveolus is a single microscopic air sac in the lung, whereas an acinus is the larger functional unit comprising all the airways and alveoli distal to one terminal bronchiole.